I made a few attempts at hacking analog sticks with hard spring controllers.
One such device was my custom Sinistar controller. It uses a Rubber "X" made out of bike inner tubes... as the
center spring.
However, the pressures that were created.. caused the entire shell of the stick to warp and finally break apart.
Eventually I found a sturdy enough shell. I believe it was the Foxfire pro or something like that... by thrustmaster.
It had very small pots.. the kind that are probably put into those thunbsticks these days. And the assembly was very rigid, with a strong shaft. I further increased that strength, but inserting a metal shaft into the cut down plastic shaft. After that.. is was solid as a rock.
Also note, you wouldnt want to hack a cheese stick for yoke handles.. because they often have horrible buttons.. with high fatigue pressure levels. As well as very thin plastic that creaks and warps under even mild strain. Its best to feel the thing first, and see if its flex and buttons are decent.. as well as the comfort of the grip. Often the grip may fit one hand well.. but feel really bad for someone else.
Analog shifters are great IMO, because they can be configured in so many ways.. and not have so many costly and failable mechanical parts. They are smooth as glass.. and silent in activation.
Take a look at Race Drivins shifter. Its quite simple but ingenious. Its a shaft welded to a door hinge! The hinge is on a shaft that rocks back and forth.. and the shifter is on the other side of the hinge.. to swing left to right. They use simple crank arms to drive pots.
On the middle pivot shaft, they have a spring loaded roller wheel. As the shifter is moved, the wheel rotates, and when in place, the spring-wheel locks into a small half-circle pit.
Its actually quite simple and fairly cheap to build. You wouldnt even need to weld it.. as you could use epoxy putty.. and or just screw the shaft to the hinge itself.
The most expensive thing is merely the metal shafts.. but you could break apart nearly anything for them.. and or just spend the 7$ at the hardware store for them.
Do remember, that shifters tend to be Slammed very hard into gear... because the action gets intense. Without decent shaft strength and good strong mechanical design.. the unit will tear itself to pieces in a few uses tops.